Each year around the world, more than 200 million people use illegal drugs -- and marijuana still appears to be the drug of choice, researchers found.

Action Points

Explain that a study analyzing other systematic reviews estimated that 149 to 271 million people worldwide used illicit drugs in 2009, with cannabis by far the most common.

Note that use seemed to be highest in high-income countries and those near to drug production areas.

Each year around the world, more than 200 million people use illegal drugs, and marijuana still appears to be the drug of choice, researchers found.

Although illegality makes accurate estimates a challenge, data from 2009 suggest that 149 to 271 million people around the world used illegal drugs, according to Louisa Degenhardt, PhD, of the University of New South Wales in Sydney, and Wayne Hall, PhD, of the University of Queensland in Australia.

Pot use, with anywhere from 125 to 203 million people lighting up annually is the most widely used, they said.

They reported their estimates in a special issue of The Lancet that focused on addiction.

That proportion is far larger than the 14 to 56 million estimated to use amphetamines, the 14 to 21 million estimated to use cocaine, and the 12 to 21 million estimated to use opioids, they found.

Pot is also the most widely used illegal drug in the U.S., according to the latest data from the Substance Abuse and Mental Health Services Administration (SAMHSA). In 2010, about 22.6 million Americans used illicit drugs, with 17.4 million of them reporting cannabis use.

Yet marijuana is the least likely of all illicit drugs to cause death, the researchers said, cautioning that it's still likely associated with dependence and mental disorders.

Opioids (heroin, fentanyl), on the other hand, are a major cause of death due to overdose and dependence, and have also been tied to HIV and hepatitis B and C infection, especially among injection-drug users.

Preference for drugs varies geographically, with pot and cocaine use highest in North America and Europe, while more than half of opioid users lived in Asia, with the highest levels being along the main drug trafficking routes out of Afghanistan.

"Levels of illicit drug use seem to be highest in high-income countries and in countries near major drug production areas," Degenhardt and Hall wrote. They noted that their study didn't assess use of hallucinogens, inhalants, benzodiazepines, anabolic steroids or ecstasy (3,4-methylenedioxymethamphetamine or MDMA).

Initiation and progression of drug use also varies by region, with most users in high-income countries starting out with alcohol and tobacco, then transitioning to marijuana use, and finally into other drugs.

But that pattern isn't consistent, the researchers said. In Japan, for instance, other illicit drug use is more prevalent than cannabis use, suggesting that abuse depends on social factors and drug availability.

"Social norms have a very powerful impact on drug use patterns," Bruce Goldman, director of substance abuse services at North Shore LIJ in Glen Oaks, N.Y., told MedPage Today in an email. "We need to create norms where substance use and availability, especially for young people, is not acceptable."

Although problematic, the global burden of disease caused by illicit drug use is far less than that of alcohol and tobacco, according to various estimates. One from 2000 found drug use to be associated with 102,000 to 322,000 deaths worldwide -- far lower than the estimated 1.8 million deaths due to alcohol use and 4.8 million deaths with tobacco use.

Similarly, World Health Organization data from 2004 suggested that 250,000 deaths worldwide were attributable to drug use, compared with 2.25 million due to alcohol use and just over five million associated with tobacco, they reported.

Still, Degenhardt and Hall called illicit drug use a "substantial global cause of premature mortality and morbidity."

They added that the 11 to 21 million people around the world estimated to inject drugs are responsible for the largest burden of disease associated with illegal drugs, along with those who are dependent; about 15 to 39 million people are thought to be in this class of "problematic" user, they reported.

They said much of this burden can be reduced or prevented through needle exchange programs, opioid substitution treatment, and antiretroviral therapy.

Many questions about global drug use remain unanswered, they added, concluding that "until we have better answers to these questions, statements about the exact magnitude of the health, social, and financial burden of illicit drug use cannot be made with accuracy."

The editors of The Lancet noted in an accompanying commentary that policymakers in the U.S. need to pay particular attention to abuse of prescription drugs.

"Prevention and treatment of prescription drug dependency offer challenges that differ from those of addiction to illicit drugs, and need innovative solutions," they wrote. "Addiction is a complex disease without a universal policy approach or treatment."

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